Sunday, August 1, 2010

A newly described, profusely feathered dinosaur may give lift to scientists’ understanding of bird and flight evolution, researchers report. The lithe creature, which stood about 28 centimeters tall at the hip, is the oldest known to have sported feathers and is estimated to be between 1 million and 11 million years older than Archaeopteryx, the first known bird.

Several fossils of the creature, which has been dubbed Anchiornis huxleyi, have been unearthed in northeastern China, Xing Xu reported September 25 at the annual meeting of the Society of Vertebrate Paleontology. The strata that contained those feathered fossils were laid down as sediments between 151 million and 161 million years ago, he and his colleagues note online September 24 in Nature.

Two types of feather adorn the creature, said Xu, of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing. One kind, commonly referred to as “dino-fuzz,” resembles a frayed bundle of filaments. The other type, similar in overall structure to the feathers of modern-day birds, consists of small filaments that branch from a larger shaftlike filament.

The dino-fuzz decorates the creature’s head and neck. About two dozen of the shafted feathers adorn each forelimb, and a similar number embellish each lower leg and foot, the researchers report. Unlike most feathered dinosaurs described previously, which have the longest forelimb feathers near the tip of the limb, Anchiornis’ longest forelimb feathers are on the wrist, Xu said. Feathers on the legs and feet appear to have overlapped each other, creating aerodynamic surfaces that would have, in essence, given Anchiornis a wing on each of its four limbs. A similar configuration has been seen in other feathered dinosaurs, including Microraptor (SN: 1/27/07, p. 53) and Archaeopteryx (SN: 9/23/06, p. 197).

With so many species with this arrangement, the four-winged configuration must have been an important phase in the evolutionary transition from dinosaurs to birds, says James M. Clark, a vertebrate paleontologist at George Washington University in Washington, D.C.

Larry D. Martin, a paleontologist at the University of Kansas in Lawrence, agrees. The profuse plumage on Anchiornis’ feet, he notes, also suggests that the creature was a tree dweller, bolstering the notion that flight developed from the trees down, not from the ground up. “No dinosaur could walk well with feathers on its feet like that,” he adds.

Many scientists scoff at the suggestion that the filamentary structures found on some dinosaurs, especially those unearthed in China in recent years, represent nascent feathers. But those creatures lived many millions of years after Archaeopteryx, which had feathers indistinguishable from those on modern-day birds. The new find is important because it undoubtedly includes the oldest known feathers on any creature, says Mike Benton, a vertebrate paleontologist at the University of Bristol in England and cochair of the Society of Vertebrate Paleontology meeting.

“These exceptional dinosaur fossils provide us with evidence that has been missing until now,” Xu said. “Now it all fits neatly into place, and we have tied up some of the loose ends.”

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Dinosaurs Fossils

Dinosaur fossils have been known about for millennia, though their true nature was not recognized; the Chinese considered them to be dragon bones, while Europeans believed them to be the remains of giants and other creatures killed by the Great Flood.